1. Field of Invention
The present invention relates to a structure of a color liquid crystal display (LCD) and a method of producing the same. More particularly, the present invention relates to a method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate and the LCD structure fabricated by the same method.
2. Description of Related Art
Liquid crystal is a material having properties between those of crystal and liquid. The alignment of the liquid crystal molecules varies with external stimulation such as an electrical field generated by an applied voltage. Hence, this feature of the liquid crystal molecules can be utilized to create a display unit.
Liquid crystal material was discovered in 1888, and applications thereof first appeared in 1963. However, the value of the commercial application was not proved until Sharp in Japan developed a liquid crystal display applied in a calculator. Japanese companies have continued to develop the technology and improve the product's function. Development and improvement have made the liquid crystal display widely applicable.
The thin-film-transistor (TFT) array substrate and the color filter substrate are fabricated separately and then are assembled in current technology for producing a color thin film transistor liquid crystal display (TFT-LCD). As a result of the limitations of assembling precision, the aperture ratio of the TFT-LCD cannot be effectively increased. Based on the limitations described above, the latest developments have led to a color filter layer being formed on a TFT array substrate by photolithography to form a color filter on array (COA) substrate. The subsequent process is only to assemble the COA substrate and a transparent indium tin oxide (ITO) substrate, with no precision limit on the assembling step. Therefore, the aperture ratio of the TFT-LCD can be greatly increased to decrease the power consumption. This is the application trend for future portable products.
The black matrixes and photoresist spacers have to be separately formed by two photolithography steps for a TFT-LCD made by the COA technique described above. If the black matrixes and the photoresist spacers are formed by only one photolithography step, only black resin of the negative photosensitive type can be used and the thickness of black resin needed is at least 5 μm. However, the light transmittance and the photosensitivity of the black resin are reduced and the required exposure dose is about 250 mj/cm2. In comparison with black resin, the required exposure dose is only about 19 mj/cm2 for a common transparent photoresist. Therefore, a very long exposure time is needed for patterning the black resin to form an ideal pattern, and the throughput of the stepper is seriously affected. Moreover, spacers are in charge of maintaining the distance between two transparent substrates; hence certain requirements exist on the shape and the height of the spacers. Consequently, the process margin for developing the black resin of the negative photosensitive type is very narrow.